The regioselective fluorination of organic compounds is an important challenge in the synthesis of pharmaceuticals and agrochemicals (see, for example, Muller et al., Science 2007, 317, 1881-1886; Park et al., Annual Review of Pharmacology and Toxicology 2001, 41, 443-470; Bohm et al., ChemBioChem 2004, 5, 637-643; and Jeschke, ChemBioChem. 2004, 5, 570-589).
Syntheses of simple fluoroarenes currently rely on the pyrolysis of diazonium tetrafluoroborates (Balz, G.; Schiemann, G. Ber. Deut. Chem. Ges. 1927, 60, 1186-1190), direct fluorination using highly reactive, elemental fluorine (Sandford, J. Fluorine Chem. 2007, 128, 90-104), or nucleophilic aromatic substitution reactions of electron—poor aromatic systems by displacement of other halogens or nitro groups (Sun et al., Angew. Chem., Int. Ed. 2006, 45, 2720-2725; Adams et al., Chem. Soc. Rev. 1999, 28, 225-231). The reductive elimination of arylfluorides from palladium(II) fluoride complexes is an attractive potential alternative that has been investigated by Grushin (Grushin, Chem.—Eur. J. 2002, 8, 1006-1014) over the past decade and more recently by Yandulov. A single substrate—p—fluoronitrobenzene—has been prepared successfully in 10% yield in the Yandulov study from a stoichiometric palladium fluoride complex (Yandulov et al., J. Am. Chem. Soc. 2007, 129, 1342-1358) (See also Watson et al., Science, 2009, Vol. 325. No. 5948, pp. 1661-1664). Directed electrophilic fluorination of phenylpyridine derivatives and related structures using catalytic palladium(II) acetate and N-fluoropyridinium salts has been reported by Sanford in 2006 (Hull et al., J. Am. Chem. Soc. 2006, 128, 7134-7135). Taking advantage of the directing effect of a pyridine substituent, proximal carbon-hydrogen bonds can be fluorinated using microwave irradiation at high temperatures (100-150 ° C., 1-4 h, 33-75% yield).
The use of 18F-labelled organic compounds for positron-emission tomography (PET) requires the controlled, efficient introduction of fluorine into functionalized molecules (see, for example, Couturier et al., Eur. J. Nucl. Med. Mol. Imaging 2004, 31, 1182-1206; Lasne et al., “Chemistry of beta(+)-emitting compounds based on fluorine-18” In Contrast Agents II, 2002; Vol. 222, pp 201-258; and Phelps, Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 9226-9233). PET has been used to measure presynaptic accumulation of 18F-fluorodopa tracer in the dopaminergic regions of the brain (see, for example, Ernst et al., “Presynaptic Dopaminergic Deficits in Lesch-Nyhan Disease” New England Journal of Medicine (1996) 334:1568-1572), but fluorination of other organic compounds has been difficult due to lack of an appropriate fluorination method.
Despite the utility of fluorinated organic compounds in multiple pharmaceutical, diagnostic, and agrochemical applications, C—F bond formation remains a challenging organic transformation with no broadly applicable solutions.